Unquoting does not work when not imported

``` r
variable <- ~cyl
lazyeval::f_interp(~ mean(uq(variable)))
## Error in lazyeval::f_interp(~mean(uq(variable))) : 
##   could not find function "uq"
```

``` r
lazyeval::f_interp(~ mean(lazyeval::uq(variable)))
## ~mean(lazyeval::uq(variable))
```

``` r
uq <- lazyeval::uq
lazyeval::f_interp(~ mean(uq(variable)))
## ~mean(cyl)
```

Probably the second snippet is a bug?
